1. Field of the Invention
The present invention relates generally to a device for inductively detecting electrically conductive objects, and, more particularly, to a search coil assembly for use in such devices.
2. Description of Related Art
Inductive search devices are used for detecting objects of electrically conductive material which are hidden from sight as they are, e.g., buried, in the soil or are surrounded by other materials having a lower electrical conductivity. It is possible with such devices either to pass the search device over a surface to be scanned as well as to pass goods to be tested past a stationary search device. In either case, an electrical signal voltage is generated as a result of the relative movement between the objects sought and the search device, such voltage being transformed into a signal capable of human detection, e.g., an acoustic or optical signal.
Search coil assemblies of the aforementioned species are known in the art in various embodiments. For example, there is known an American mine search device, wherein the receiver coil of the search coil assembly has four partial coils connected pair-wise in opposition to each other and arranged in a common plane. Such partial coils are received in depressions of a plate-type housing, which are located at the four corners of a square. The disadvantage of this search coil assembly is that deformation of the housing caused by thermal or other influences will immediately affect the position of the individual receiver coils with respect to one another and their position with respect to the energizing or excitation coil. This will result in lack of stability and in a permanent drift of the output voltage of the receiver coils. Another disadvantage is the heavy weight of such a search coil assembly. Furthermore, it is disadvantageous that the partial coils must be rather accurately identical in their coil characteristics requiring high precision of winding.